LMX2571: Synchronizing multiple devices

Part Number: LMX2571
Other Parts Discussed in Thread: LMX2594, LMX2572

Tool/software:

Hello, I was wondering if there is a method to synchronize multiple LMX2571 devices across different boards if they are all clocked with the same Reference Oscillator.

Is there an order in which to program the SPI bus registers that would help with this? 

Is there a method to reset the fractional counters together?

What if they were programmed on the same exact SPI signals in parallel?

What if the devices are booted without the reference clock, programmed with SPI, then introduced the Reference Oscillator at the same time?

If all of the above methods will not synchronize the part, do you offer a similar synthesizer chip that has an external reset that can synchronize the fractional dividers?

I can see that my multiple LMX2571s are PLL locked with eachtoher, but they sometimes wake up out of phase. I have to issue full board reset to sometimes get lucky and have the devices wake up locked and in phase.

  • Hi David,

    there are restrictions on multiple synthesizers synchronization, not every frequency is able to synchronize. 

    Our LMX2572, LMX2594 are design to support synchronization, restrictions still apply to certain configuration.

    Please refer to LMX2572 datasheet section 7.3.11 and section 8.1.6 for details.

  • Thank you, I will look into using the LMX2572 in the next revision.

    To my previous questions: Toggling Chip enable on the same bus and/or programming the SPI on the same bus will not sync and reset two different device's divide counters at the same time?

  • Hi David,

    Correct, toggling the CE pin will not do any reset to the counter.